A conventional speed reducer with an electric motor that includes an electric motor and a speed reducer and decelerates the power obtained from the electric motor and outputs the power is known. FIG. 5 is a diagram schematically illustrating a structure of a conventional speed reducer 1X with an electric motor. The speed reducer 1X with an electric motor has an electric motor 20X, a speed reduction mechanism 30X, and an output part 40X that rotates at a decelerated rotation speed. In the example of FIG. 5, however, the electric motor 20X, the speed reduction mechanism 30X, and the output part 40X are disposed in the direction of the center axis 9X (the axial direction) of the electric motor 20X. For this reason, the dimension of the speed reducer 1X with an electric motor in the axial direction becomes longer. Therefore, the speed reducer 1X with an electric motor having the structure of FIG. 5 is unsuitable for applications with severe restrictions on dimensions in the axial direction, like joint parts of working robots and assist suits, turntables, wheel-in dividing plates, and the like.
In order to restrict the dimension of the speed reducer with an electric motor in the axial direction, for example, providing the electric motor around a rotation axis and disposing the speed reduction mechanism on the outer circumference side of the electric motor in a concentric shape are considered. In that way, the electric motor and the speed reduction mechanism are disposed at a position in the same axial direction, and thus the speed reducer with the electric motor can have a thin shape in the axial direction as a whole. Patent Literature 1, for example, discloses such a conventional speed reducer with an electric motor in which a speed reduction mechanism is disposed on an outer circumference side of the electric motor.
[Patent Literature 1]
Japanese Utility Model Publication No. S60-166259